Nickel-hydride battery life determining method and life determining apparatus

ABSTRACT

Data indicating a relationship of life of a battery to a value of load power applied to the battery in discharge and environmental temperature of a place where the battery is installed are prepared beforehand. Next, the load power and the environmental temperature when the battery is discharged are measured, and then a life value corresponding to these measured values is selected from the data so as to be set as an expected life value. Next, a first life reduction amount is calculated from a natural logarithmic function with the number-of-discharges as a variable, and the difference between the expected life value and the first life reduction amount is set to a remaining life value, on the basis of which the life of the nickel-hydride battery is determined. By this method, the life of the nickel-hydride battery as a backup power source can be accurately determined, while correction based on phenomena unique to the nickel-hydride battery is performed.

TECHNICAL FIELD

The present invention relates to a life determining method of anickel-hydride battery used for an uninterruptible power supply and thelike, and a life determining apparatus adopting the method, and moreparticularly to a precise life determining method based on a behaviorunique to the nickel-hydride battery.

BACKGROUND ART

In an apparatus incorporating a backup battery such as anuninterruptible power supply (UPS), it is important to detect the lifeof the battery from the viewpoint of maintenance and inspection. Ingeneral, the deterioration of life of a nickel-hydride battery is mainlycaused by corrosion of a hydrogen storage alloy of a negative electrode,but is often influenced by such factors as the use temperature, thenumber-of-discharges, the magnitude of load power in discharge, and thelike. In this way, the factors for determining the life of the batteryare diversified, and hence, it is not easy to accurately determine thelife of the battery in use.

Conventionally, it is proposed to use an increase in the internalresistance at the end of life of the battery and a voltage change indischarge as parameters in order to determine the life of anickel-hydride battery. For example, there are disclosed an apparatuswhich performs deterioration determination by calculating a gradient ofdischarge voltage values based on the distribution of the dischargevoltage values corresponding to plural discharge current values (forexample, patent document 1), and an apparatus which performsdeterioration determination by relatively comparing values of internalresistance and battery voltage which are measured during discharge withtheir initial values (for example, patent document 2). In these lifedetermination methods, attention is directed to a correlation of theinternal resistance of the battery with the resultant voltage change andlife of the nickel-hydride battery, and hence, these methods areeffective in that it is possible to estimate the life of the battery tosome degrees in a short period time.

On the other hand, there is proposed a method in which an expected lifevalue of a battery is calculated from a discharge load power value andin which the difference between the expected life value and a lifereduction amount calculated as a linear function with thenumber-of-discharges as a variable is used as a remaining life value todetermine the life of the battery (for example, patent document 3). Thismethod makes it possible to use a highly precise expected life value bysuitably correcting the value without forcibly making the batterydischarge, and hence, is effective for a lead-acid battery, and thelike.

Patent document 1: Japanese Laid-Open Patent Publication No. 8-138759

Patent document 2: Japanese Laid-Open Patent Publication No. 2000-215923

Patent document 3: Japanese Laid-Open Patent Publication No. 2000-243459

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

However, in the methods disclosed in the patent documents 1 and 2, it isimpossible to perform the life determination unless the internalresistance is increased to some extent. Further, in the methods, thedischarge frequency, the battery temperature and the like which becomecauses of the life deterioration are not taken into consideration.Further, in the method disclosed in patent document 3, the formula usedfor the life determination is not a linear function with thenumber-of-discharges as a variable because of the deterioration behavior(corrosion of the hydrogen storage alloy of the negative electrode)unique to the nickel-hydride battery. For this reason, in any case,there is a problem that the remaining life value is considerablydeviated from the actual record value.

The principal object of the invention is to provide a method foraccurately determining the life of a nickel-hydride battery and anapparatus adopting the method.

Means for Solving the Problem

A first life determining method of a nickel-hydride battery according tothe present invention comprises:

(a) a step of preparing beforehand data representing a relationship oflife of the battery to load power applied to the battery in dischargeand environmental temperature of a place in which the battery isinstalled;

(b) a step of measuring the load power and the environmental temperatureof the battery in discharge;

(c) a step of selecting a life value corresponding to the measuredvalues of the load power and the environmental temperature from the datato set the life value as an expected life value;

(d) a step of calculating a first life reduction amount from a naturallogarithmic function with the number-of-discharges of the battery as avariable; and

(e) a step of setting a value obtained by subtracting the first lifereduction amount from the expected life value to a remaining life value.

As described above, the main cause of deterioration of life of anickel-hydride battery is corrosion of a hydrogen storage alloy of anegative electrode. The hydrogen storage alloy is rapidly selfpulverized owing to the volumetric change in accordance with storage anddischarge of hydrogen in the initial charge and discharge. At this time,corrosion of the hydrogen storage alloy is accelerated, but thecorrosion is suppressed in accordance with the settlement of the selfpulverization after the number-of-discharges is increased. In contrastto a battery system such as a lead-acid battery in which charge anddischarge are repeated by the dissolution and deposition of activematerials, the life deterioration as a behavior unique to thenickel-hydride battery is expressed by a natural logarithmic functionwith the number-of-discharges as a variable.

The present invention, in which attention is directed to this behavior,is to provide a life determining method capable of accuratelydetermining the life of the nickel-hydride battery.

Specifically, when the expected life value is L₀, thenumber-of-discharges is N, the first life reduction amount is L₁, andthe remaining life value is L, then the first life reduction amount isexpressed by the following formula (1), and the remaining life value isexpressed by the following formula (2):

L ₁ =a×ln(b×N)+c  (1)

L=L ₀ −L ₁  (2)

where a, b, c are constants, and in represents the natural logarithmicfunction.

Since the life reduction amount increases in accordance with the degreeof corrosion of the hydrogen storage alloy of the negative electrode, L₁becomes small when the constitution condition of the battery is changedto suppress the corrosion or to reduce the effect of the corrosion. Notethat the values of a, b of the constants a, b, c are changed by theconstitution of the nickel-hydride battery, for example, by thethickness of the separator, but the value of c is almost constant in thenickel-hydride battery.

A second life determining method according to the present invention is amethod capable of more accurately determining the life of anickel-hydride battery, and in the above described first method, furthercomprises: a step of calculating an average value of batterytemperatures measured at a fixed time interval during charge anddischarge or during pause of the charge and discharge; a step ofcalculating a second life reduction amount from the product of thenumber-of-discharges and a value of an exponential function with thedifference between the average value of battery temperature and themeasured value of environmental temperature as a variable; and a step ofperforming life determination by using a value obtained by subtractingthe first and second life reduction amounts from the above describedexpected life value as a remaining life value.

The life of the nickel-hydride battery is exponentially reduced inaccordance with the temperature rise of the battery itself. This isbecause corrosion of the hydrogen storage alloy is more acceleratedunder the high temperature than the normal temperature. By adding thisfactor to the first method according to the present invention, the lifeof the nickel-hydride battery can be more accurately determined.

Specifically, when the expected life value is L₀, the first lifereduction amount is L₁, the number-of-discharges is N, the average valueof the battery temperatures measured at a fixed time interval duringcharge and discharge or during pause of the charge and discharge isT_(m), the environmental temperature at the time of calculating theexpected life value is T₀, the second life reduction amount is L₂, andthe remaining life value is L, then the second life reduction amount isexpressed by the following formula (3), and the remaining life value isexpressed by the following formula (4):

L ₂ =d×N×2^([(Tm-T0)/10])  (3)

L=L ₀−(L ₁ +L ₂)  (4)

where d is a constant.

Since the second life reduction amount L₂ is changed in accordance withthe average value of battery temperature, L₂ becomes small when theconstitution condition of the battery is changed to suppress heatgeneration and to improve heat dissipation. Note that the constant d isan almost fixed value depending upon the kind of the battery.

A third life determining method according to the present invention is amethod capable of more accurately determining the life of anickel-hydride battery, and in the above described second method,further comprises: a step of calculating a non-periodical expected lifevalue from the product of the initial expected life value and a value ofan exponential function with the difference between the measured valueof environmental temperature and the average value of batterytemperature as a variable; and a step of performing life determinationby using a value obtained by subtracting the first and second lifereduction amounts from the non-periodical expected life value as aremaining life value.

More strictly, the above described expected life value L₀ in the firstand second methods (having the same meaning as the initial expected lifevalue) is exponentially changed with the temperature history of thebattery. By adding this factor to the second method according to thepresent invention, the life of the nickel-hydride battery can be moreaccurately determined.

Specifically, when the initial expected life value is L₀, thenon-periodical expected life value is L_(m), the first life reductionamount is L₁, the environmental temperature at the time of calculatingthe initial expected life value is T₀, the average value of batterytemperature during charge and discharge or during pause of the chargeand discharge is T_(m), the second life reduction amount is L₂, and theremaining life value is L, then the non-periodical expected life valueis expressed by the following formula (5) and the remaining life valueis expressed by the following formula (6).

L _(m) =L ₀×2^([(T0-Tm)/10])  (5)

L=L _(m)−(L ₁ +L ₂)  (6)

In the above described third method according to the present invention,in order to calculate a life value from a value of load power applied toa nickel-hydride battery in discharge, data indicating a relationship oflife of the battery to load power and environmental temperature areprepared beforehand, and a life value corresponding to measured valuesof load power and environmental temperature is selected from the data soas to be set as the expected life value, as a result of which the lifeestimation can be performed more accurately. Further, in the case wherethe nickel-hydride battery is performing its original backup functionowing to real power interruption, correction relating to the batterylife deteriorated by the discharge is performed, so that the life of thebattery can be more precisely and accurately determined.

Next, a life determining apparatus of a nickel-hydride battery accordingto the present invention comprises:

storing means which stores data indicating a relationship of life of thebattery to load power applied to the battery in discharge andenvironmental temperature in a place where the battery is installed;

load power measuring means which measures the load power applied to thebattery;

environmental temperature measuring means which measures theenvironmental temperature;

expected life value selecting means which selects as an expected lifevalue, a life value corresponding to the load power and theenvironmental temperature which are measured, from the data stored inthe storing means;

number-of-discharges counting means which counts thenumber-of-discharges of the battery;

first life reduction amount calculating means which calculates a firstlife reduction amount from a natural logarithmic function with thenumber-of-discharges counted by the number-of-discharges counting meansas a variable; and

remaining life value calculating means which calculates a remaining lifevalue from the difference between the expected life value and the firstlife reduction amount.

In the above described life determining apparatus according to thepresent invention, the influence of the backup discharge during powerinterruption upon the life of the battery can be reflected in the lifedetermination of the battery by utilizing the first life reductionamount.

A life determining apparatus according to the present invention, inaddition to the above described constitution, further comprises:

battery temperature measuring means which measures battery temperaturesduring charge and discharge or during pause of the charge and dischargeat a fixed time interval;

average value calculating means which calculates an average value ofbattery temperature from the measured battery temperatures and thenumber of measurement; and

second life reduction amount calculating means which calculates a secondlife reduction amount from the product of the number-of-discharges and avalue of an exponential function with the difference between the averagevalue of the battery temperature and the environmental temperature as avariable.

In the above described life determining apparatus according to thepresent invention, the battery temperature can be reflected in the lifedetermination of the battery by calculating the remaining life valuefrom the difference between the expected life value and the first andsecond life reduction amounts, so that the accuracy of remaining lifevalue can be further improved.

A life determining apparatus according to the present invention, inaddition to the above described constitution, further comprises

non-periodical expected life value calculating means which selects alife value of battery corresponding to the measured load power and themeasured environmental temperature from the data stored in the storingmeans to set the selected life value as an initial expected life value,and which calculates a non-periodical expected life value from theproduct of the initial expected life value and a value of an exponentialfunction with the difference between the environmental temperature andthe average value of the battery temperature as a variable.

In the above described life determining apparatus according to thepresent invention, the expected life value can be optimized as needed bycalculating the remaining life value from the non-periodical expectedlife value, the first life reduction amount, and the second lifereduction amount, as a result of which the accuracy of the remaininglife value can be further improved.

The above described life determining apparatus according to the presentinvention, can be made to function as a more efficient system byintegrating each means of the life determining part with the battery, orby additionally providing means for displaying the remaining life value,means for communicating the remaining life value, or means forcontrolling the charging of the battery on the basis of the remaininglife value.

EFFECT OF THE INVENTION

The life determining method and apparatus of a nickel-hydride batteryaccording to the present invention is capable of precisely andaccurately determine the life of a nickel-hydride battery incorporatedin an uninterruptible power supply, even in the case where the dischargepower, the discharge frequency, the battery temperature and the like aredifferent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a life determining apparatus of anickel-hydride battery according to the present invention;

FIG. 2 is a flow chart showing a life determining method of anickel-hydride battery in an embodiment 1 according to the presentinvention;

FIG. 3 is a flow chart showing a life determining method of anickel-hydride battery in an embodiment 2 according to the presentinvention; and

FIG. 4 is a flow chart showing a life determining method of anickel-hydride battery in an embodiment 3 according to the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, embodiments according to the present invention will bedescribed with reference to the accompanying drawings. Note that thepresent invention can be practiced with proper modification withoutdeparting from the scope of the invention.

FIG. 1 is a block diagram showing a life determining apparatus accordingto the present invention. In FIG. 1, a life determining apparatus 1 isconstituted of a life determining part 2 and a nickel-hydride battery 3incorporated in an uninterruptible power supply.

In the life determining part 2, there are incorporated: load powermeasuring means 4 which measures a value of load power; storing means 5which stores data of a relationship between load power and battery lifeobtained beforehand at a fixed interval of environmental temperature inthe form of a load power-battery life table; environmental temperaturemeasuring means 6 which measures an environmental temperature of a placewhere the battery 3 is installed; expected life value calculating means7 which selects an expected life value from the life data stored in thestoring means 5 on the basis of the load power measured by the loadpower measuring means 4, and the environmental temperature measured bythe environmental temperature measuring means 6; number-of-dischargescounting means 8 which counts the number-of-discharges of the battery 3;battery temperature measuring means 9 which measures batterytemperatures at a fixed time interval; average value calculating means10 which calculates an average value by dividing the sum of the batterytemperatures measured by the battery temperature measuring means 9 bythe number of times of the measurements; remaining life displaying means11 which displays a remaining life; a control part 12; charging controlmeans 13; and communication means 14.

The control part 12 comprises: first life reduction amount calculatingmeans 12 a which converts information from the number-of-dischargescounting means 6 counting the number-of-discharges to a life reductionamount; second life reduction amount calculating means 12 b whichconverts the average value of battery temperature obtained by theaverage value calculating means 10 and information from thenumber-of-discharges measuring means 8 to a life reduction amount;non-periodical expected life value calculating means 12 c whichcalculates a non-periodical expected life value by adding theinformation from the average value calculating means 10 to an initialexpected life value read from the storing means 5; and remaining lifevalue calculating means 12 d. Note that reference numeral 15 denotes anuninterruptible power supply unit body.

Next, each life determining method according to the present inventionwhich uses the above described life determining apparatus will bespecifically explained on the basis of a flow chart.

Embodiment 1

FIG. 2 is a flow chart showing a first life determining method accordingto the present invention.

When the nickel-hydride battery 3 incorporated in the uninterruptiblepower supply starts to discharge, the life determining apparatus 1starts operating, so that an operation (route A) to obtain an initialexpected life value L₀, and an operation (route B) to obtain a firstlife reduction amount L₁ are started.

The operation of route A is explained. A relationship between load powerapplied to the battery in discharge and battery life is obtainedbeforehand at each fixed interval of environmental temperature, and dataof the relationship are stored as a load power-battery life table 20 inthe storing means 5 such as a memory.

First, an environmental temperature T₀ of a place where the battery 3 isinstalled is measured by the environmental temperature measuring means 6(step S21), and then a load power value is measured by the load powermeasuring means 4 (S22). Normally, a load power value is expressed by atime rate of discharge current representing a discharge rate.

Next, the measured value of load power is collated with a value of theload power-battery life table 20 stored in the storing means 5 (S23),and an expected life value L₀ corresponding to the load power value isobtained from a table closest to the environmental temperature measuredin S21. Then the obtained expected life value L₀ is outputted to thecontrol part 12 (S24).

Next, the operation of route B is explained. The number-of-discharges Nof the battery 3 is obtained by the number-of-discharges counting means6 (S25). The value N is outputted to the control part 12, and a firstlife reduction amount L₁ is obtained as a natural logarithmic functionwith the number-of-discharges N as a variable by the formula (1) in thefirst life reduction amount calculating means 12 a, and outputted (S26).Then, on the basis of the initial expected life value L₀ and the firstlife reduction amount L₁ which are obtained, the remaining life value Lis calculated by the formula (2) in the remaining life value calculatingmeans 12 d (S27).

The remaining life value L obtained in this way is outputted to theremaining life displaying means 11 from the control part 12, so as toinform a user of the remaining life by lighting LED and the like, bydisplay on a display and the like, or by emitting a sound and the like.The remaining life value L is further sent to the uninterruptible powersupply unit body 15 by the communication means 14, so that the chargingof the nickel-hydride battery 3 which is currently discharged iscontrolled by the charging control means 13.

Note that since the nickel-hydride battery is generally installed in aplace where the battery is hardly seen by the user, it is effective toprovide the remaining life displaying means 11 in a part which can beeasily seen by the user similarly to the control part of theuninterruptible power supply unit body.

Embodiment 2

FIG. 3 is a flow chart showing a second life determining methodaccording to the present invention.

In the second life determining method according to the presentinvention, an operation of route C is added to the operation of routesA, B explained in the first life determining method. In the operation ofroute C, similarly to the route A, an environmental temperature T₀ isfirst measured by the environmental temperature measuring means 6 (S31),and the battery temperature is measured at every fixed time interval bythe battery temperature measuring means 9. Thereafter, an average valueT_(m) of the battery temperature is calculated in the average valuecalculating means 10 (S32). A second life reduction amount L₂ iscalculated by the formula (3) using the average value T_(m) of batterytemperature, the environmental temperature T₀, and thenumber-of-discharges N already measured in S25 in the route B (S33).Then, on the basis of the expected life value L₀, the first lifereduction amount L₁, and the second life reduction amount L₂ which areobtained, a remaining life value L is calculated by the formula (4) inthe remaining life value calculating means 12 d (S34). The succeedingprocessing is similar to that of the first embodiment, and hence theexplanation thereof is omitted.

Embodiment 3

FIG. 4 is a flow chart showing a third life determining method accordingto the present invention.

In the third life determining method, the operation up to the step (S24)which calculates the initial expected life value L₀ in the operation ofroute A is the same as the operation in the first and second lifedetermining methods, but the following operation is different from theoperation in the first and second life determining methods.Specifically, the non-periodical expected life value calculating means12 c calculates a non-periodical expected life value L_(m) from theformula (5) using the environmental temperature T₀ measured in S21, andthe average value T_(m) of battery temperature calculated in S32 of theroute C (S41). Then, in the remaining life value calculating means 12 d,a remaining life value L is calculated to determine the life of thenickel-hydride battery by subtracting the first life reduction amount L₁and the second life reduction amount L₂ from the obtained non-periodicalexpected life value L_(m) (S42). The succeeding processing is similar tothat of the embodiment 1.

Next, in relation to the above described life determining methodaccording to the present invention, examples in which the remaining lifevalue is calculated under various conditions on the basis of each of theabove described formulas, are explained.

EXAMPLE 1

A positive electrode formed by filling spherical nickel hydroxide powderinto three-dimensional porous nickel and a negative electrode formed byapplying hydrogen storage alloy powder to a nickel plated punching metalare combined so as to make their theoretical capacity ratio to ½ (theratio of the negative electrode to the positive electrode is set to 2).Then, the electrodes are wound with a separator made of a sulfonatedpolypropylene nonwoven fabric so that an electrode group is formed. Thiselectrode group is inserted into a nickel plated cylindrical iron can.After an electrolyte consisting of an aqueous solution of KOH and NaOHis poured into the can, the opening of the can is sealed with a sealingplate and a gasket. In this way, a cylindrical nickel-hydride battery Ahaving a diameter of 17 mm, a height of 50 mm, a separator thickness of0.18 mm and the nominal capacity of 1800 mAh is produced.

This battery A is incorporated in the life determining apparatus shownin FIG. 1. Then, after the nickel-hydride battery integrated with thelife determining apparatus is subjected to a sufficient number ofinitial activation cycles, the following charge and discharge test forthe battery is performed under an atmosphere at 40° C. The expected lifevalue (initial expected life value) L₀ is calculated in comparison withthe life information of the battery extracted beforehand from therelationship between the environmental temperature and the dischargecurrent value.

Charge at 900 mA, stop the charge at the voltage drop of 5 mV from themaximum achievable voltage (so-called, −ΔV control system), and pausefor 3 days.

The above charge and pause cycle is repeated, and the discharge isperformed at the discharge current of 1800 mA to a voltage of 1.0 V oncefor every ten cycles. At each point of time when the discharge isrepeated 10 times, 30 times and 50 times, the remaining life value L iscalculated on the basis of the flow chart shown in FIG. 2. In the lifedetermining apparatus, the end of the life of the nickel-hydride batteryis determined at the point of time when the remaining capacity of thebattery reaches 1080 mAh (60% of the nominal capacity).

The expected life value L₀, the environmental temperature and thedischarge rate (represented by a time rate) which are used at the timeof calculating the expected life value L₀, and values of the constantsa, b, c in the formula (1) used for life determination are shown in No.1 in Table 1. The calculation result of the remaining life value isshown in No. 1 of Table 2.

EXAMPLE 2

With the life determining apparatus in the example 1, the discharge rateis changed to the time rate ×5 and the time rate ×0.5, so that theremaining life value L is calculated on the basis of the flow chartshown in FIG. 2. The condition for calculating the expected life valueL₀ and values of the constant a, b, c are shown in Nos. 2 and 3 of Table1, and the calculation results of the remaining life value L is shown inNos. 2 and 3 of Table 2, respectively.

COMPARATIVE EXAMPLE 1

With the life determining apparatus and the battery of the example 1,the remaining life value is calculated under the same conditions as theexamples 1, 2 by using a linear function (L=L₀−N) instead of theformulas (1) and (2). The conditions for calculating the remaining lifevalue and the calculation results are shown in Nos. 9 to 11 of Tables 1and 2, respectively.

EXAMPLE 3

With the life determining apparatus and the battery of the example 1,the remaining life value L is calculated on the basis of the flow chartshown in FIG. 3 by using the formulas (3), (4). The condition includingthe value of the constant d in the formula (3) for calculating theremaining life value and the calculation result are shown in No. 4 ofTables 1 and 2, respectively.

EXAMPLE 4

With the life determining apparatus and the battery of the example 1,the remaining life value L is calculated on the basis of the flow chartshown in FIG. 4 by using the formulas (5), (6). The condition forcalculating the remaining life value and the calculation result areshown in No. 5 of Tables 1 and 2, respectively. Note that the averagevalue T_(m) of the battery temperature is shown in Table 2.

EXAMPLE 5

With the life determining apparatus and the battery of the example 1,the remaining life value is calculated under the same condition as theexample 1 except that the environmental temperature is changed to 35° C.The condition for calculating the remaining life value and thecalculation result are shown in No. 6 of Tables 1 and 2, respectively.

COMPARATIVE EXAMPLE 2

With the life determining apparatus and the battery of the example 5,the remaining life value is calculated by using the linear function(L=L₀−N). The condition for calculating the remaining life value and thecalculation result are shown in No. 12 of Tables 1 and 2, respectively.

EXAMPLE 6

A cylindrical nickel-hydride battery B having the same constitution asthat of the example 1 except that the thickness of separator is 0.18 mmand the nominal capacity is 1600 mAh, and a cylindrical nickel-hydridebattery C having the same constitution as that of the example 1 exceptthat the thickness of separator is 0.26 mm and the nominal capacity is1400 mAh, are produced. The remaining life values of these batteries arecalculated under the same condition as that of the example 1. Thecondition for calculating the remaining life value and the calculationresults are shown in Nos. 7 and 8 of Tables 1 and 2.

COMPARATIVE EXAMPLE 3

With the life determining apparatus and the battery of the example 6,the remaining life value is calculated by using the linear function(L=L₀−N). The condition for calculating the remaining life value and thecalculation result are shown in Nos. 13 and 14 of Tables 1 and 2.

TABLE 1 Environmental Time temperature rate L₀ Formula for No. Battery(° C.) (×) (Cycle) determination a b c d 1 A 40 1 60 (Formulas 1, 2)10.9 0.05 −0.11 — 2 A 40 5 72 (Formulas 1, 2) 10.9 0.05 −0.11 — 3 A 400.5 40 (Formulas 1, 2) 10.9 0.05 −0.11 — 4 A 40 1 60 (Formulas 3, 4)10.9 0.05 −0.11 0.14 5 A 40 1 60 (Formulas 5, 6) 10.9 0.05 −0.11 0.14 6A 35 1 85 (Formulas 1, 2) 10.9 0.05 −0.11 — 7 B 40 1 73 (Formulas 1, 2)12.1 0.09 −0.11 — 8 C 40 1 90 (Formulas 1, 2) 15.2 0.22 −0.11 — 9 A 40 160 L₀-N — — — — 10 A 40 5 72 L₀-N — — — — 11 A 40 0.5 40 L₀-N — — — — 12A 35 1 85 L₀-N — — — — 13 B 40 1 73 L₀-N — — — — 14 C 40 1 90 L₀-N — — ——

The deviation of the remaining life values L obtained in each of theexamples and the comparative examples as described above from theactually measured values are shown by the number of cycles for eachnumber-of-discharges N in Table 2.

TABLE 2 N = 10 N = 30 L₁ T_(m) L₂ L_(m) L Deviation L₁ T_(m) L₂ L_(m)No. (Cycle) (° C.) (Cycle) (Cycle) (Cycle) (Cycle) (Cycle) (° C.)(Cycle) (Cycle) 1 −8 — — — 68 −12 4 — — — 2 −8 — — — 80 −12 4 — — — 3 −8— — — 48 −23 4 — — — 4 −8 40 1 — 67 −13 4 40 4 — 5 −8 40 1 60 67 −13 440 4 60 6 −8 — — — 93 −7 4 — — — 7 −1 — — — 74 −14 12 — — — 8 12 — — —78 −22 29 — — — 9 — — — — 50 −30 — — — — 10 — — — — 62 −30 — — — — 11 —— — — 30 −41 — — — — 12 — — — — 75 −25 — — — — 13 — — — — 63 −25 — — — —14 — — — — 80 −20 — — — — Actually N = 30 N = 50 measured L Deviation L₁T_(m) L₂ L_(m) L Deviation value No. (Cycle) (Cycle) (Cycle) (° C.)(Cycle) (Cycle) (Cycle) (Cycle) (Cycle) 1 56 −4 10 — — — 50 10 90 2 68−4 10 — — — 62 10 102 3 36 −15 10 — — — 30 −1 81 4 52 −8 10 41 8 — 42 290 5 52 −8 10 41 8 56 38 −2 90 6 81 1 10 — — — 75 15 110 7 61 −7 18 — —— 55 7 98 8 61 −19 36 — — — 54 −6 110 9 30 −30 — — — — 10 −30 90 10 42−30 — — — — 22 −30 102 11 10 −41 — — — — −10 −41 81 12 55 −25 — — — — 35−25 110 13 43 −25 — — — — 23 −25 98 14 60 −20 — — — — 40 −20 110

It can be seen from Table 2 that the deviation of the values of thecomparative examples shown in Nos. 9 to 14 from the actually measuredvalues is significant, while the deviation of the values of the examplesshown in Nos. 1 to 8 from the actually measured values is small. Thistendency is more significant as the number-of-discharges N is increased.As a reason for this tendency, it is considered that corrosion of thehydrogen storage alloy is settled by the repetition of the cycles andthereby can be approximated by a natural logarithmic function.

Specifically, in the case of the present embodiment, this tendency isconsidered to be influenced by the fact that the battery is constitutedso as to make the negative electrode theoretical capacity twice thepositive electrode theoretical capacity, and thereby the lifedeterioration speed of the battery greatly deviates from the linearfunction to get closer to the natural logarithmic function.

Also, as a reason for the fact that the determination results in Nos. 4and 5 are more accurate than those in Nos. 1 to 3 as thenumber-of-discharges N is increased, it is considered that the heatgeneration resulting from charge and discharge and the change ofenvironmental temperature can be more easily taken into account.

In the present embodiment, a metallic battery can with relatively highheat dissipating characteristic is used, but in the case where a batterycase made of a resin with relatively low heat dissipatingcharacteristic, the effect of determination based on the formulas (3),(4) and the formulas (5), (6) is considered to become more remarkable.

Further, in the present embodiment, the intermittent charging based onthe −ΔV control system is selected as the battery charging method, butsubstantially the same effect can also be obtained even when theintermittent charging based such as on the dT/dt control system which isa temperature control system and on the timer control system isperformed, or when the trickle charging is performed.

INDUSTRIAL APPLICABILITY

The life determining method and apparatus according to the presentinvention are useful in the life determining method of a nickel-hydridebattery used for example for an uninterruptible power supply and thelike, and in the life determining apparatus using the method.

1-2. (canceled)
 3. A life determining method of a nickel-hydridebattery, comprising the steps of: (a) preparing beforehand datarepresenting a relationship of life of the battery to load power appliedto the battery in discharge and environmental temperature of a placewhere the battery is installed; (b) measuring the load power and theenvironmental temperature of the battery in discharge; (c) selecting alife value corresponding to the measured values of the load power andthe environmental temperature from the data to set the life value as aninitial expected life value; (d) calculating an average value of batterytemperatures measured at a fixed time interval during charge anddischarge or during pause of the charge and discharge, to calculate anon-periodical expected life value from the product of the initialexpected life value and a value of an exponential function with thedifference between the measured value of environmental temperature andthe average value of battery temperature as a variable; (e) calculatinga first life reduction amount from a natural logarithmic function withthe number-of-discharges of the battery as a variable; (f) calculating asecond life reduction amount from the product of thenumber-of-discharges and a value of an exponential function with thedifference between the average value of battery temperature and themeasured value of environmental temperature as a variable; and (g)setting a value obtained by subtracting the first life reduction amountand the second life reduction amount from the non-periodical expectedlife value to a remaining life value. 4-13. (canceled)
 14. A lifedetermining apparatus of a nickel-hydride battery, comprising: storingmeans which stores data indicating a relationship of life of the batteryto load power applied to the battery in discharge and environmentaltemperature in a place where the battery is installed; load powermeasuring means which measures the load power applied to the battery;environmental temperature measuring means which measures theenvironmental temperature; expected life value selecting means whichselects a life value corresponding to the load power measured by theload power measuring means and the environmental temperature measured bythe environmental temperature measuring means from the data stored inthe storing means as an initial expected life value;number-of-discharges counting means which counts thenumber-of-discharges of the battery; first life reduction amountcalculating means which calculates a first life reduction amount from anatural logarithmic function with the number-of-discharges counted bythe number-of-discharges counting means as a variable; batterytemperature measuring means which measures battery temperatures duringcharge and discharge, or during pause of the charge and discharge at afixed time interval; average value calculating means which calculates anaverage value of battery temperature from battery temperatures measuredby the battery temperature measuring means and the number ofmeasurements; non-periodical expected life value calculating means whichcalculates a non-periodical expected life value from the product of avalue of an exponential function with the difference between theenvironmental temperature measured by the environmental temperaturemeasuring means and the average value of battery temperature calculatedby the average value calculating means as a variable, and the initialexpected life value selected by the expected life value selecting means;second life reduction amount calculating means which calculates a secondlife reduction amount from the product of a value of an exponentialfunction with the difference between the average value of batterytemperature calculated by the average value calculating means and theenvironmental temperature measured by the environmental temperaturemeasuring means as a variable, and the number-of-discharges counted bythe number-of-discharges counting means; and remaining life valuecalculating means which calculates a remaining life value by subtractingthe first life reduction amount calculated by the first life reductionamount calculating means and the second life reduction amount calculatedby the second life reduction amount calculating means from thenon-periodical expected life value calculated by the non-periodicalexpected life value calculating means.
 15. The life determiningapparatus of a nickel-hydride battery according to claim 14, whereineach of the means is integrally provided for the battery.
 16. The lifedetermining apparatus of a nickel-hydride battery according to claim 14,further comprising means for displaying the remaining life value. 17.The life determining apparatus of a nickel-hydride battery according toclaim 14, further comprising means for communicating the remaining lifevalue.
 18. The life determining apparatus of a nickel-hydride batteryaccording to claim 14, further comprising means for controlling chargeof the battery on the basis of the remaining life value.